"Mass gatherings have been associated with death and destruction - catastrophic stampedes, collapse of venues, crowd violence and damage to political and commercial infrastructure."

Prof Brian McCloskey, who is in charge of the Health Protection Agency's preparations for London 2012, told the BBC: "The history of the Olympic Games suggests infection doesn't happen often.

"The issue for us is to make sure the right system is in place to respond."

He has been improving the agency's disease surveillance to include data straight from hospitals and walk-in centres, which he said would "leave a legacy of probably the most comprehensive disease surveillance system in the world".